Scanners are photolithography tools used to form patterns on substrates such as semiconductor substrates, i.e. wafers. Scanners are considered a type of stepper and are used to create millions of microscopic circuit elements on the substrate surface. A die or chip typically includes millions of these microscopic circuit elements that combine to form an integrated circuit or other semiconductor device. Each substrate includes hundreds or even thousands of individual die.
The microscopic circuit elements that combine to form an integrated circuit or other semiconductor device, are produced in a pattern of transparent and opaque areas on the surface of a quartz plate called a reticle. The scanner passes light through the reticle, projecting an image of the reticle pattern onto the substrate. The image is focused and reduced by a lens and projected onto the surface of the substrate that is coated with a photosensitive material called photoresist. The reticle may include one die or chip, or it may include a cell of multiple die, as its exposure field. The multiple die that combine to form the cell that appears on the reticle, may be the same die or the die may differ from one another. In steppers, the image of the reticle is projected onto the substrate during the exposure operation which includes exposing the entire exposure field during each exposure “shot”. The exposure field may include an individual die or cell of multiple die, as above. A scanner does not expose the entire field at once but rather exposes the substrate through an exposure slit that is generally at least as wide as the exposure field, but only a fraction of its length. The stage holding the substrate is translated relative to the fixed exposure slit so that the entire exposure is projected from the reticle onto the substrate as the beam scans across the die and the substrate. Subsequent manufacturing operations such as developing, form a photomask out of the photoresist material after the image from the exposure field of the reticle has been projected onto the photoresist. The photomask is used in subsequent processing operations.
A substrate typically includes the individual die or chips arranged in columns and rows. The operation of patterning an entire substrate to produce hundreds or thousands of die that are arranged in the rows and columns, is a time-consuming operation. This time-consuming operation must be carried out at multiple device levels in the sequence of fabrication operations used to form an integrated circuit or other semiconductor device.
It would therefore be advantageous to reduce the time required to expose an entire substrate using a scanner.